Various specialized medical devices, such as ablation devices, cardiac leads, ultrasonic catheters, balloon angioplasty catheters, electrophysiological diagnostic catheters, pressure monitoring catheters, etc., may require the use of a delivery system for deploying the device in a desired internal body space, such as the heart, for example. In addition, in some cases, dissection of tissue is desired or necessary to guide or deliver such specialized medical devices to a desired location.
Although the present invention contemplates devices and systems for dissecting tissue and/or guiding other specialized medical devices to many areas of the body, in particular, the present application will focus on one exemplary desired location and one exemplary specialized medical device. The focus will be primarily on delivery of an ablation device to an area on or near the heart, which, in particular, is around the two separate pairs of pulmonary veins on both sides of the heart. Similarly, the present invention contemplates the use of the present inventive devices and systems to treat various conditions. However, in particular, the present application will focus on treatment for heart arrhythmias (e.g., atrial fibrillation) using ablation procedures.
In a normal heart, contraction and relaxation of the heart muscle (myocardium) takes place in an organized fashion as electrochemical signals pass sequentially through the myocardium from the sinoatrial (SA) node located in the right atrium to the atrialventricular (AV) node and then along a well-defined route which includes the His-Purkinje system into the left and right ventricles. Sometimes abnormal rhythms occur in the atrium which are referred to as atrial arrhythmia. Three of the most common arrhythmias are ectopic atrial tachycardia, atrial fibrillation, and atrial flutter. Arrhythmia can result in significant patient discomfort and even death because of a number of associated problems, including the following: (1) an irregular heart rate, which causes a patient discomfort and anxiety; (2) loss of synchronous atrioventricular contractions, which compromises cardiac hemodynamics resulting in varying levels of congestive heart failure; and (3) stasis of blood flow, which increases vulnerability to thromboembolism. It is sometimes difficult to isolate a specific pathological cause of the arrhythmia, although it is believed that the principal mechanism is one or a multitude of stray circuits within the left and/or right atrium. These circuits or stray electrical signals are believed to interfere with the normal electrochemical signals passing from the SA node to the AV node and into the ventricles.
Treatment of arrhythmias may be accomplished by a variety of approaches, including drugs, surgery, implantable pacemakers/defibrillators, and catheter ablation. While arrhythmic drugs may be the treatment of choice for many patients, these drugs may only mask the symptoms and do not cure the underlying cause. Implantable devices, on the other hand, usually can correct an arrhythmia only after it occurs. Surgical and catheter-based treatments, by contrast, may actually cure the problem usually by ablating the abnormal arrhythmogenic tissue or abnormal pathway responsible for the arrhythmia. The catheter-based treatments rely on the application of various destructive energy sources to the target tissue including direct current energy sources to the target tissue, including direct current electrical energy, radiofrequency electrical energy, microwave energy, laser energy, cryoenergy, ultrasound, and the like.
One surgical method of treating arrhythmia is the “Maze” procedure, which relies on a prescribed pattern of incisions to anatomically create a convoluted path, or maze, for electrical propagation within the left and right atria. The procedure employs incisions in the right and left atria, which divide the atria into electrically isolated portions, and which in turn results in an orderly passage of a depolarization wave front from the SA node to the AV node, while preventing reentrant wave front propagation. The Maze procedure has been effective in curing arrhythmias, but the procedure is technically difficult. The procedure also requires open heart surgery, in which the breastbone is divided and the surgeon has direct access to the heart.
More recently, Maze-like procedures have been developed utilizing ablation catheters that can form lesions on the endocardium to effectively create a maze for electrical conduction in a predetermined path. Typically, the lesions are formed by ablating tissue with an electrode carried by a catheter. Ablative energy, e.g., high intensity focused ultrasound (HIFU) energy, radiofrequency (RF) energy, microwave energy and/or laser energy, applied to the electrode, causes significant physiological effects in the tissue resulting from thermal and/or mechanical changes or effects. By controlling the energy level, the amount of heat generated in the tissue and the degree of tissue damage or change can also be controlled. Ablation uses lower levels of voltage that creates sufficient heat to cause a desired cell damage, but leaves the tissue structure intact so as to effectively block electrical pathways within the tissue. Irrigation of the electrode(s) with saline or other conductive fluid can decrease the interface impedance, cool the tissue, and allow for a greater lesion depth.
A treatment for atrial fibrillation, in particular, includes ablation around the pulmonary veins, which procedure is called pulmonary vein antrum isolation. Almost all the atrial fibrillation signals are believed to come from the four pulmonary veins and move to the atria. Ablation of the area of the atria that connects to the pulmonary veins provides circular scar tissue that blocks impulses firing within the pulmonary veins from moving to the atria, thereby disconnecting the pathway of abnormal rhythm and preventing atrial fibrillation.
Most ablation devices are designed to access the heart via a mid-line sternotomy. More recently, ablation of cardiac tissue can be carried out through a minimally invasive route, such as between the ribs, through a sub-xyphoid incision or via catheter that is introduced through a vein, and into the heart. Such minimally invasive procedures are generally performed off-pump, which means the heart is beating during the procedure. Such procedures accordingly require several ports for medical devices to enter the area of the heart and perform the procedures.
Ablation of a precise location within the heart requires precise placement of an ablation device within or near the heart. Precise positioning of the ablation device is especially difficult because of the physiology of the heart, particularly as such recently developed procedures generally occur off-pump. As discussed earlier, in some cases, dissection of tissue is necessary to guide or deliver specialized medical devices to their desired location in the body. In particular, with regard to pulmonary vein antrum isolation, tissue connecting each pair of pulmonary veins to pericardial reflections is often dissected allowing ablation device placement on and/or around the pulmonary veins.
In general, if prior art devices for dissection are used, and if guidance of a specialized medical device to a location after the dissection is desired, separate devices are used for dissection and for placing the specialized medical device. Prior art devices that allow for both dissection and placement of another device, in particular with regard to ablation devices, require suturing a catheter at or near the end of the device while the end of the device is near the heart. Suturing near a beating heart involves risk of negative consequences.
Thus, there is a need for an improved device that can dissect tissue and guide specialized medical devices to particular locations in the body. In particular, an improved device and method for dissecting cardiac tissue and placement of ablation devices during minimally invasive procedures on a beating heart are desired.